The present application relates generally to the field of airbags in automotive vehicles. More specifically, this application relates to an airbag configured to have improved cushion seams to reduce weight and cost, while maintaining strength.
It has been known to construct an airbag for use in a vehicle having an airbag cushion formed by coupling two or more panels together. It has been known to use a seam to couple at least two airbag cushion panels, where the seam includes sewing stitches, typically made of a plurality of stitches made of 400-2400 denier thread or yarn, to reduce or prevent separation (i.e., relative movement) of the coupled panels. It has further been known to apply an adhesive or sealant to the adjacent and interconnected surfaces of the panels to prevent inflation gas from escaping through the plurality of apertures (or holes) created by the plurality of stitches made of thread forming the stitching, as well through the needle holes. These airbags are configured so that the sewing stitches provide the strength or structural integrity of the seam, while the sealant fills and seals the gaps between the airbag cushion panels and stitches. Accordingly, for an optimized design, the airbag is typically configured so that the strength of the stitching and the strength of the panel are substantially similar. To increase the strength of the sewing stitches, the thread diameter or size may be increased, or a material with a higher tensile strength may be used. To increase the strength of the fabric panels of the airbag cushion, a higher denier (i.e., weight) panel may be used or the panel may be made from a higher strength material.
The primary disadvantage of airbags configured using sewing stitches to provide the structural integrity of the seam, is that the sewing stitches produce holes or voids in the fabric panels of the airbag cushion from the sewing needles, which reduce the strength of the airbag panel local to the seam, so the panel must be overdesigned, typically through an increase in fabric thickness (i.e., denier) or in fabric strength, to accommodate this strength degradation at the seam. The panel strength degradation occurs local to the seam when the stitching is applied, since the stitching produces a hole or void in the airbag panel for each pass of the thread or yarn. Each needle hole produces a stress concentration in the panel local to the hole when under load, and often under the high temperature and high stress that the panel is subjected to during deployment, holes will begin to elongate, which propagates tearing of the panel. The reduced strength of the panel local to the stitching influences the entire panel to be designed to accommodate the local high stress seam region, and since the seam area is typically a small percentage of the total cushion area, the panel is overdesigned and inefficient. A seam having sewing stitches, which joins two layers or two panels of the same fabric, has been found to reduce the strength of the panels by 60% relative to a single sheet of the same fabric having no stitching.